NIT

The possibility of getting an NIT  in 100 marks is low but you can get it if you have state quota as well as your OBC category reservation. But there is still your medium level good chances of getting into nits.

You can get medium level branches in lower NIT's.

As top NIT'S have higher marks requirement of higher branches of CSE, IT, ECE.

Yes, you could appear for the JEE entrance test and apply to NITs, provided you have completed the 12th standard through the Assam State Open Schooling and your qualification is recognised by the authorities. Normally, a candidate should have completed the 12th standard with Physics, Chemistry, and Mathematics, and scored more than 75% (or be among the top 20 percentile in the board examination). It is advised to ascertain JBIC officials about the board's recognition status if you are to be considered an eligible candidate. 

With a CRL rank of 159865 and an OBC rank of 53541, you are unlikely to get admission into a top NIT for a popular branch, but you might be able to secure a seat in a newer NIT for a less preferred branch using your OBC category rank; it's best to check the closing ranks of different NITs and branches on the JoSAA website to see your chances

For admissions to NITs/ IIITs/ GFTIs, candidates should have secured at least 75% marks in class 12th exam or be in the top 20 percentile in the class 12th exam conducted by the respective board. For SC/ ST candidates, the eligibility criteria are 65% marks in class XII.

Congratulations on clearing JEE Mains and JEE Advanced. 

For getting Admission in IIT  Class 12th 75% Percentage marks in mandatory without 75% you are not eligible for getting admission in IIT.

 NIT AND IIT Both criteria is similar.

Firstly, clear all your fundamentals about all the chapters in all 3 subjects. You should be knowing major concepts and their applications.

Practice Mock tests and sample papers- Candidates must practice more and more JEE Main sample papers and mock tests. These mock tests and sample papers will open the candidates to different types of questions daily and will help them analyze their performance.

Try to solve every question in under 2minutes so that during exam, you'll get more time to crosscheck your answers.

All the very best :).

A rank of 1788 in JEE Mains with a percentile of 74.15% makes admission to an NIT possible but difficult. The cutoff ranks vary across branches and categories for different NITs. The cutoff for popular branches such as Computer Science or Electronics will be high, while that for Civil or Mechanical will be easier to crack based on the category and availability of seats. You should be alert to any changes in the trend pattern as reported in the counseling process (JoSAA) for your category and branch preference.